The impact type of riveting, where rivet heads are formed by an impacting gun operating against a bucking tool, has been largely replaced with a squeeze type of riveting, where the rivet is formed between a pair of anvils or dies that axially approach each other to deform the rivet by a squeezing force.
U.S. Pat. No. 3,557,442 to Speller shows squeeze forming of a rivet blank using upper and lower annular clamps and coaxial upper and lower head-forming anvils. The upper anvil is fixed and the lower anvil squeezes the rivet blank upward to partially form the lower head, then move the work piece and rivet blank upward to form the upper head and complete head formation of the lower head. Initially the force of the upper clamp exceeds the force of the lower anvil, but after partial forming of the lower rivet head, the lower anvil force becomes greater and the work piece is moved upward.
It is also known to use a pogo stick arrangement attached to an upper anvil, wherein the resistance to retraction of the pogo stick is greater than the force on the lower anvil until the lower head of a rivet is partially formed.
It was found that holding the work piece between a pair of resilient members held by the forming tools gives simultaneous instead of stepped rivet head formation.